It is a misconception that black people do not get drunk as easily as white people. If you think that your black friends are not getting as drunk as your white friends, it may be that your black friends did not drunk as much or they drank a different type of alcohol that has a lower proof. Higher proof alcohol will get you drunk faster. It also could be that your black friends are just as drunk as your white friends but they are just acting differently.
Your white friends may have fewer inhibitions to start with and when they are a little drunk their inhibitions are even lower, making them appear more drunk. Not every person reacts to alcohol in the same way but race is not a factor.